sclass AudioAdder implements IAudioSample {
  new Cl<IAudioSample> sources;
  gettable double sampleRate;
  settable int channels;
  settable DoubleRange bounds;
  
  // for now same value in all channels
  new TreeMap<Double> additions;
  
  *() {}
  *(IAudioSample source) { addUnlessNull(sources, source); }
  
  void addSource(IAudioSample source) {
    addUnlessNull(sources, source);
    this.source = source;
  }
  
  void addPlateau(double start, double end, double intensity) {
    if (start >= end) ret;
    
    _changeSumAt(start, intensity);
    _changeSumAt(end, -intensity);
  }

  // We will probably add plateaus rather randomly throughout an area,
  // so could optimize this doing something akin to LogNArray.
  void _changeSumAt(double time, double intensity) {    
    double value = unnull(floorValue(additions, time)) + intensity;
    
    // create, overwrite or delete
    mapPutOrRemove(additions, time, nullIfZero(value));
    
    Double next = additions.higherKey(time);
    while (next != null) {
      subtractions.put(next, additions.get(next) + intensity);
      next = subtractions.higherKey(next);
    }
  }
  
  public double readSumTable(int channel, double t) {
    double diff = unnull(floorValue(additions, t));
    ret diff;
    for (source : sources) diff += source.readSumTable(channel, t);
    ret diff;
  }
}